The present invention generally relates to ink-jet printing, and in particular to a specific form of Reactive Red 23 magenta dye which is hydrolyzed to produce a passivated form with better pH stability thus improving kogation, decap and lighffastness.
The use of inkjet printing systems has grown dramatically in recent years. This growth may be attributed to substantial improvements in print resolution and overall print quality coupled with appreciable reduction in cost. Today""s ink-jet printers offer acceptable print quality for many commercial, business, and household applications at costs fully an order of magnitude lower than comparable products available just a few years ago. Notwithstanding their recent success, intensive research and development efforts continue toward improving ink-jet print quality. In general, ink-jet print quality still falls short of that produced by more expensive technologies such as photography and offset or gravure printing. A surge in interest in ink-jet imaging (e.g., the rendition of pictures) has resulted in the need to produce near photographic quality printed images at a reasonable cost. The challenge remains to further improve the image quality and lighffastness of ink-jet printed images, especially images containing skin tones, without increasing their cost.
If such an ink is to be used in an ink-jet printing device, characteristics such as crusting, long-term stability, and materials compatibility must also be addressed. If the ink is to be used in a thermal ink-jet printer, the further constraint of being thermally stable (kogation-resistant) is added.
In general, a successful ink set for color ink-jet printing must be compatible with the ink-jet pen and printing system. Some of the required properties for the ink-jet ink include: good crusting resistance, good stability, the proper viscosity, the proper surface tension, little color-to-color bleed, rapid dry time, no negative reaction with the vehicle, high solubility of the dyes in the vehicle, consumer safety, low strike through, high color saturation, and good dot gain. Color ink-jet printers typically use three inks of differing hues: magenta, yellow, and cyan. Optionally black is also used. EP 662499 and EP 366121 both assigned to Canon disclose the use of Reactive Red 23 in inkjet ink.
The present invention relates to a high lightfastness magenta dye comprising hydrolyzed Reactive Red 23 with from 0 to 100% hydroxy form and from 0 to 100% vinyl form: 
The present invention further relates to a set of ink-jet inks for ink-jet printing, at least one of the inks being a magenta ink comprising a high lightfastness magenta dye, the high lightfastness magenta dye comprising hydrolyzed Reactive Red 23 with from 0 to 100% hydroxy form and from 0 to 100% vinyl form: 
The present invention additionally relates to a method of making a passivated form of Reactive Red 23 comprising hydrolyzing Reactive Red 23 to obtain hydrolyzed Reactive Red 23 with from 0 to 100% hydroxy form and from 0 to 100% vinyl form 
The present invention described herein is directed to ink-jet inks for printing inkjet images using commercially available ink-jet printers such as, for example but not limited to, HP DeskJet(copyright) printers, manufactured by Hewlett-Packard Company, of Palo Alto, Calif. The inks enable production of near photographic images having little or no coalescence, excellent waterfastness, and reduced dry time, on a range of print media, in particular, for example but not limited to, plain white, 8 xc2xdxe2x80x3xc3x9711xe2x80x3, 20 lb. weight, printer paper conventionally used for office and home computers.
RR23 is a very lightfast dye. The reactive portion of this dye molecule will hydrolyze over time in an aqueous solution. It is known that when the reactive group of other inkjet dyes (Reactive Red 180 and Reactive Black 31) is hydrolyzed overtime, pH instability over the life of the ink has resulted. The pH change and salts formed during hydrolysis over time increase the occurrence of kogation, decap and lighffastness problems in an ink containing a reactive dye .
The present inventor has found that when RR23 is passivated initially by hydrolyzing the reactive sulfate group of the dye that a more stable dye results with better characteristics of pH stability, kogation, decap and lightfastness. The passivation can occur under acid or alkaline conditions. In a preferred embodiment the passivation occurs under alkaline conditions and in a more preferred embodiment the passivation occurs at a pH of at least 9.
In one embodiment, the present invention relates to a high lighffastness magenta dye comprising hydrolyzed Reactive Red 23 with from 0 to 100% hydroxy form and from 0 to 100% vinyl form: 
In a preferred embodiment of the high lighffastness magenta dye of the present invention, at least 50% of the hydrolyzed Reactive Red 23 is the hydroxy form.
In another embodiment, the present invention relates to a set of ink-jet inks for ink-jet printing, at least one of the inks being a magenta ink comprising a high lightfastness magenta dye, the high lightfastness magenta dye comprising hydrolyzed Reactive Red 23 with from 0 to 100% hydroxy form and from 0 to 100% vinyl form: 
In a preferred embodiment of the set of ink-jet inks of the present invention, at least 50% of the hydrolyzed Reactive Red 23 is the hydroxy form.
In another preferred embodiment of the set of ink-jet inks of the present invention, at least one of the inks is a cyan ink comprising a cyan dye; and at least one of the inks is a yellow ink comprising a yellow dye.
In yet another embodiment, the present invention relates to a method of making a passivated form of Reactive Red 23 comprising hydrolyzing Reactive Red 23 to obtain hydrolyzed Reactive Red 23 with from 0 to 100% hydroxy form and from 0 to 100% vinyl form. 
In a preferred embodiment of the method of the present invention, hydrolyzing the Reactive Red 23 is conducted at a pH of at least 9.
In another preferred embodiment of the method of the present invention, at least 50% of the hydrolyzed Reactive Red 23 is the hydroxy form.